1. Field of the Invention
The present invention relates to a composite multilayer substrate that is used in the manufacture of multilayered IC's or multichip modules.
2. Description of the prior art
It is well known in the prior art to utilize a thin film structure that can be formed from multilayers of either high or low temperature pre-fired or co-fireable ceramic green tape with power and ground connections between the multilayers. The so-called co-fireable ceramic tape is a flexible substrate in the green (unfired) state before heating and is manufactured by various companies including DuPont who sells its product under the trademark Greentape. The thin and flexible material becomes rigid after it is subjected to heat as by firing in an oven. Typically this greentape is commercially available for use with high density packages of IC's. In some cases, a high temperature plastic material, such as polyimides, are used as a substrate for co-fireable structures.
Electrically conductive circuits are screen printed or otherwise deposited on the dielectric substrate. Connections between layers of the substrate that are aligned and stacked are made by forming vias and filling with a conductive material. The substrates are typically machined or formed; fired if necessary and drilled using mechanical tools, lasers or chemical etching. Both active and passive components are attached individually onto the substrates, which substrates have suitable dielectric thermal and physical properties, and are connected electrically to the circuit by proper placement and soldering by using conductive cements.
Often the circuits, including printed resistors and layered capacitors, are fired before other components are attached to each substrate and the substrates aligned, stacked, packaged and tested.
Current multilayered IC's or multichip modules have low manufacturing yields and premature field failures due to substrate cracks, conduit electrical shorts and poor component adhesion to the substrate. These problems increase the number of layers required and increase component density. Often the vias will crack as a result of material expansion mismatch, residual stress in the substrate and poor via filling.